Process for the preparation of ether carboxylic acids from carbohydrates and derivatives thereof and their use

ABSTRACT

A process for the preparation of ether carboxylic acids by ethoxylation of carbohydrates followed by catalytic oxidation and the use of the products in detergents or cleaning agents.

DESCRIPTION

The present invention relates to a process for the preparation of ethercarboxylic acids by ethoxylation of carbohydrates, followed by catalyticoxidation, and to the use of the products obtained.

Owing to their eutrophying effect in lakes and rivers, the use ofphosphates in detergents and cleaning agents has become restricted bylaw and in some cases even prohibited in a number of countries. As aresult, a large number of substitutes for phosphates, in particular forsodium tripolyphosphate, have been developed and proposed in themeantime as builder. However, the desirable properties of sodiumtripolyphosphate in its application as a detergent have hitherto notbeen achieved entirely by any single substance. Rather, onlycombinations of builders are capable of achieving in a firstapproximation the effect of phosphates. Only a relatively small numberof phosphate substitutes, or rather partial substitutes, are fullysatisfactory with respect to their ecological properties. Although theydo not promote eutrophication of lakes and rivers, they havenevertheless in some cases properties which must be regarded asquestionable in their effect on the environment, such as remobilizationof heavy metals from sediments of the lakes and rivers or insufficientbiological degradability; therefore, their effect on the environment isuncertain, even if these substances do not immediately have to beconsidered toxic according to current knowledge. Accordingly, the searchfor effective builders for detergents which can be considered safe withrespect to their ecological effect continues.

In JP-A2-58/117,284 so-called viscosity-reducing agents of coal sludgesare disclosed, which can be prepared by reaction of polyhydric alcohols,which also include carbohydrates, with alkylene oxides to give polyethercompounds, followed, if desired, by conversion of the terminal hydroxylgroups into carboxyl groups; however, more detailed information on thesynthesis of these products is not given.

Ethoxylation of carbohydrates has been known for quite a long time.Thus, for example, W. Gerhardt, J. f. prakt. Chem., 4th series, 29, 300(1965) has described ethoxylation of saccharose; JP-A2-58/117,284 alsomentions further carbohydrates. However, economical processes for thepreparation of oxidized ethoxylates of carbohydrates and the use of suchproducts as builders are hitherto not known.

Accordingly, the object was to develop biologically degradable phosphatesubstitutes and an economical and industrially feasible method ofpreparation.

Surprisingly, it has now been found that biologically degradablephosphate substitutes having good lime-binding power are obtained byethoxylating carbohydrates, followed, if desired, by alkoxylation bymeans of a higher alkylene oxide, and converting the terminal primaryhydroxyl groups into carboxyl groups by catalytic oxidation.

Accordingly, the invention relates to a process for the preparation ofether carboxylic acids by alkoxylation of carbohydrates and derivativesthereof, followed by oxidation, which process comprises eitherethoxylating the carbohydrates or derivatives thereof directly in theusual manner or first alkoxylating them using a higher alkylene oxideand then ethoxylating them and oxidizing the aqueous solution thusobtained without any further treatment in a pH range in which thecarbohydrates and carboxylic acids derived therefrom are stable, usingoxygen as the oxidizing agent in the presence of a catalyst containingat least one platinum metal.

The invention furthermore also relates to the use of these ethercarboxylic acids in particular as additive (builder) in detergents orcleaning agents.

The ether carboxylic acids prepared by the process according to theinvention are suitable in particular as builders in detergents andcleaning agents, due to their surprisingly high lime-binding power.

Suitable starting materials are virtually any carbohydrates having atleast one alkoxylatable hydroxyl group and one alcohol group which canbe oxidized to a carboxyl group, such as glucose, galactose, maltose,lactose, fructose, β-cyclodextrin, in particular saccharose. Examples ofsuitable derivatives are α-methylD-glucoside, sorbitol, mannitol,2-desoxy-D-ribose and D-glucosamine.

Ethoxylation and alkoxylation are carried out in the usual manner, i.e.in general in aqueous solution under the action of basic catalysts attemperatures of between 50° and 150° C., preferably in a pressure rangefrom atmospheric pressure to 15 bar. The solution containing thecompounds having the terminal hydroxyethyl groups is subjected tocatalytic oxidation, preferably after dilution to a water content of70-90% by weight, resulting in the formation of the ether carboxylicacids. Advantageously, at least 50%, preferably at least 75%, and inparticular about 100%, of the hydroxyl groups of the carbohydrates andof the derivatives should be alkoxylated

Suitable higher alkylene oxides are butylene oxide, styrene oxide and inparticular propylene oxide. These can be used, for example, in an amountof up to 3 mol, advantageously of at least 0.1 mol. Naturally, thepercentage of higher alkylene oxides chosen is advantageously such thatbiological degradability is ensured.

The ethylene oxide is advantageously used in an amount of at least 1mol, for example of up to 10 mol and preferably of up to 5 mol. All moledata given refer to moles of hydroxyl groups present in the carbohydrateor the derivative thereof. If these are first reacted with an alkyleneoxide other than ethylene oxide, the total amount of the convertedalkylene oxide, i.e. including ethylene oxide, is advantageously notmore than 5 mol.

Suitable catalysts are those containing platinum metals, i.e. osmium,iridium, rhodium, ruthenium, palladium and/or platinum. Preference isgiven to catalysts containing a combination of palladium and platinumand in particular only platinum. Preferably, the platinum metals havebeen deposited on a support, such as Al₂ O₃ or SiO₂, in particular onactivated carbon. The metal content of the catalyst is in general 1 to15, preferably 5 to 10, % by weight.

Occasionally, it may be advantageous, in particular when the startingmaterials used are carbohydrate derivatives having poorer watersolubility, to add a solubilizing agent which is inert under thereaction conditions, preferably in a concentration of 10 to 75% byweight, in particular 30 to 50% by weight, relative to the amount ofwater and solubilizing agent. Suitable solubilizing agents are inparticular those which have low volatility upon passage of oxygenthrough the aqueous solution, thus substantially avoiding any risk ofexplosion in the vapor space; on the other hand, it is desirable thatthe solubilizing agent can be easily separated off after oxidation, forexample by distillation. Examples of suitable solubilizing agents areglycol ethers without free OH groups, such as those of the formula R¹ O(CHRCH₂ O)_(n) R², in which n is a number from 1 to 4, R is H or CH₃ andR¹ and R² are each, independently of one another, C₁ -C₄ -alkyl.Dimethyl ethers, diethyl ethers and methyl ethyl ethers of the generalformula mentioned and having boiling points in the range from 100° toabout 250° C., for example triethylene glycol dimethyl ether andpreferably diethylene glycol dimethyl ether, are particularly suitable.

The preferred oxidizing agent is pure oxygen. However, it is alsopossible to use mixtures of oxygen with gases which are inert under thereaction conditions, for example mixtures of oxygen with inert gases.Air itself is of course also suitable.

As a rule, the oxidation is carried out at a total pressure of 0.5 to100 bar. The reaction rate increases noticeably with increasing oxygenpartial pressure; however, the advantage of the higher reaction rate maybe overcompensated with respect to economy by the more complicatedapparatus necessary when higher pressure is applied. A pressure rangefrom atmospheric pressure to 10 bar (absolute) is preferred, it beingparticularly easy to operate at atmospheric pressure.

As a rule, oxidation is carried out at a temperature from 5° to 80° C.,preferably from 10° to 60° C., in particular from 20° to 40° C. Sincemany carbohydrates and carboxylic acids derived therefrom have lowstability in the acidic range, oxidation is advantageously carried outin an approximately neutral to weakly alkaline medium, i.e. in a pHrange from 5 to 9, preferably from 6 to 8.5 and in particular from 7 to8. The carboxylic acids formed during oxidation are advantageouslytrapped, for example by suitable buffer substances, or advantageously byaddition of aqueous bases, for example alkali metal hydroxide oralkaline earth metal hydroxide solutions, which are advantageouslymetered in in such a way that the pH of the reaction system remains inthe range from 6 to 9 during oxidation. In the case of completeneutralization, the oxidation products are obtained in the form ofsalts.

The process according to the invention can be carried out in anyapparatus which is suitable for carrying out reactions in liquid phasewith or without application of superatmospheric pressure. Examples ofthese are carrying out the reaction in a stirred reactor or in a bubblecolumn containing suspended catalyst. However, oxidation can also becarried out over a solid bed containing granular catalyst in a tricklephase reactor.

The required reaction time is advantageously determined by removingsamples of the reaction solution at certain intervals and analyzingthem. For example, the yield of the reaction products can becontinuously determined in a simple manner by analyzing a sample bymeans of high-pressure liquid chromatography by comparison with standardsolution. It is recommended to optimize the reaction time, since anunnecessarily prolonged introduction of oxygen may lead tooveroxidations and thus, for example, to decarboxylations and toreduction in the yield of the desired reaction products.

The reaction mixture can be worked up by customary methods. For example,first the water and any solubilizing agent present are removed bydistillation. Purification, for example by chromatography,crystallization or precipitation, is then carried out. It is alsopossible to separate off the product from the solution obtained duringoxidation by passing the solution through basic ion exchangers in theOH⁻ form. However, it has in general proven advantageous to subject thesolution obtained in the course of the reaction to spray-drying.

The lime-binding power of the ether carboxylic acids can be determinedby conventional analytical methods, for example by turbidimetrictitration or potentiometric titration by means of an ion-specificelectrode.

The ether carboxylic acids obtainable according to the invention aresuitable in particular as builder in detergents or cleaning agents. Inaddition, they can also be used as food additive, as crosslinking agentin paint preparations, and the like.

The examples which follow illustrate the invention.

EXAMPLE 1 Preparation

333 g of ethylene oxide were added to 111 g of sucrose and 2.75 g of KOHin 450 ml of water in a 2 1 stirred autoclave in such a manner that thetemperature was between 85° and 100° C. and the pressure was up to 4bar. After a reaction time of 2 hours, the solution was cooled to roomtemperature and made up with water to a total volume of 4 1. Afteraddition of 20 9 of a commercially available catalyst (5% of platinum onactivated carbon), this solution was gassed at 50° C. in an externallyheated upright glass tube (100 mm in diameter, 800 mm in length) frombelow through a glass frit with 100 NL/h of oxygen. The pH wasmaintained at 7 to 7.5 by continuous addition of 30% aqueous sodiumhydroxide solution. The oxidation time was 6 h. Spray-drying of thereaction product gave 390 g of a colorless powder having a lime-bindingpower of 279 mg of CaCO₃ per g of substance (determined at roomtemperature).

EXAMPLE 2 Preparation

Analogously to Example 1, 110 g of sorbitol were ethoxylated with 470 gof ethylene oxide and 4 g of KOH in 950 ml of water and then, afteraddition of 4.27 1 of water and 290 g of catalyst, oxidized. Thespray-dried product (484 g) had a lime-binding power of 373 mg of CaCO₃/g of substance.

EXAMPLE 3 Preparation

Analogously to Example 1, pentaerythritol and α-methylglucoside wereethoxylated and oxidized and, after workup, tested for theirlime-binding power. The product obtained from pentaerythritol had alime-binding power of 343 mg of CaCO₃ /g of substance and that obtainedfrom α-methylglucoside a lime-binding power of 327 mg of CaCO₃ /g ofsubstance.

EXAMPLE 4 Preparation

The superiority of the product obtained according to the invention asbuilder can be seen in the test results of detergent formulations inwhich only the saccharose tricarboxylic acid obtained according toGerman Offenlegungsschrift 3,535,720 was replaced by the productaccording to the invention of Example 1. The washing test of thesedetergents was carried out in accordance with the approved technicalrules, following DIN 44983:

The washing power (difference in reflectance) was determinedphotometrically by measuring the reflectance (colorimeter RFC 3 fromZeiss) of two WFK and EMPA test soiled fabrics at a wavelength of 460 nm(WFK=Waschereiforschungsinstitut Krefeld (Laundry Research InstituteKrefeld); EMPA=*(Swiss Material Testing Institute, Switzerland)). Inthis test, the "difference method" according to the equation:

    % R=% R.sub.g -% R.sub.u was used.

In this equation

R is % difference in reflectance (washing power),

R_(g) is % reflectance of the washed fabric

R_(u) is % reflectance of the unwashed fabric.

*Eidgenossische Materialprufanstalt

The deposit on the fabric (incrustation) was determined in the form ofinorganic fabric ash as the ignition residue in percent at 800° C.

Some of the detergent powders were prepared by the so-calledhot-spraying process and the others by the so-called spray mist mixingprocess (dry mixing process). Hot-spraying was carried out by means of alaboratory spray dryer (Buchi, type 190) with an inlet temperature ofabout 180° C., an outlet temperature of about 100° C., a sprayingpressure of 5 bar and a solids concentration of 30% by weight.

In the spray mist mixing process, a free-falling mixer was used , inwhich the liquid components were sprayed onto the pulverulent drycomponents by means of a suitable spraying device. The procedure isdescribed in detail in "Seifen, Fette, Ole, Wachse", 99, (1973),351-357.

Detergent formations and washing tests are described in the tablesbelow.

    ______________________________________                                        Detergent formulations                                                                           Spray mist mixing tests                                                       Example                                                                       Comparison                                                                              4                                                ______________________________________                                        Saccharose tricarboxylic acid (STA)                                                                10.0        --                                           (known product as described in                                                German Offenlegungsschrift 3,535,720)                                         Ether carboxylic acid according to                                                                 --          10.0                                         the invention (as Example 1)                                                  Zeolite              21.5        21.5                                         Sodium perborate tetrahydrate                                                                      20.0        20.0                                         Anionic surfactants (alkylbenzene-                                                                 7.0         7.0                                          sulfonate)                                                                    Nonionic surfactants (alkoxylated                                                                  4.0         4.0                                          alcohols)                                                                     Soaps                3.5         3.5                                          Sodium silicate      5.0         5.0                                          Carboxymethylcellulose                                                                             1.0         1.0                                          Methylcellulose      0.5         0.5                                                               Balance to 100%                                                               customary detergent                                                           components                                               ______________________________________                                    

    ______________________________________                                        Washing test according to DIN 44983 (two-liquor process,                      laundry of 60° C., water hardness 18° German hardness)          Dosage                                                                        (g)        Primary washing effect of various test fabrics                     prewash/   (% difference in reflectance)                                      Ex-   clear    EMPA cotton WFK cotton                                                                             WFK cotton                                ample wash     No. 101     No. 10C  No. 10D                                   ______________________________________                                        Com-  150/150  26          21       23                                        parison                                                                             150/150  31          27       30                                        ______________________________________                                        Washing test according to DIN 44983 (two-liquor process,                      laundry of 90° C., water hardness 18° German hardness)          Dosage                                                                        (g)                                                                           prewash/   % ash after 25 wash cycles                                         Ex-   clear                Cotton   Double-rib                                ample wash     Terry       (EMPA)   (WFK)                                     ______________________________________                                        Com-  150/150  2.1         2.3      2.4                                       parison                                                                             150/150  0.9         0.4      0.4                                       ______________________________________                                    

We claim:
 1. A process for the preparation of ether carboxylic acids byalkoxylation of carbohydrates and derivatives thereof, followed byoxidation, which comprises either ethoxylating the carbohydrate orderivatives thereof directly in the usual manner or first alkoxylatingthem using a higher alkylene oxide and then ethoxylating them andoxidizing the aqueous solution thus obtained without any furthertreatment in a pH range in which the carbohydrates and carboxylic acidsderived therefrom are stable, using oxygen as the oxidizing agent in thepresence of a catalyst containing at least one platinum metal.
 2. Theprocess as claimed in claim 1, wherein the amount of the higher alkyleneoxide is up to 3 mol and that of the ethylene oxide is from 1 to 10 mol,in each case relative to 1 mol of OH in the carbohydrate and thederivative thereof.
 3. The process as claimed in claim 1 wherein thecatalyst contains either a combination of palladium and platinum or onlyplatinum as the platinum metal.
 4. The process as claimed in claim 1wherein the catalyst comprises 1 to 15% by weight, of the platinum metaland a support, preferably activated carbon.
 5. The process as claimed inclaim 1 wherein the oxidation is carried out in a pressure range from0.5 to 100 bar.
 6. The process as claimed in claim 1 wherein the aqueoussolution contains a solubilizing agent which is inert under the reactionconditions.
 7. The process as claimed in claim 1 wherein the oxidationis carried at a temperature from 5° to 80° C.
 8. The process as claimedin claim 1 wherein the oxidation is carried out at a pH from 5 to
 9. 9.A method for using the ether carboxylic acids obtained by he process asclaimed in claim 1, comprising the step of introducing a said ethercarboxylic acid into a detergent or cleaning agent formulation as abuilder therefor.
 10. A detergent or cleaning agent, which contains theether carboxylic acids prepared as claimed in claim
 1. 11. The processas claimed in claim 2, wherein the total amount of alkylene oxide is upto 5 mol.
 12. The process as claimed in claim 4, wherein the catalystcomprises 5 to 10% by weight of the platinum metal and an activatedcarbon support.
 13. The process as claimed in claim 5, wherein theoxidation is carried out in a pressure range from atmospheric pressureto 10 bar.
 14. The process as claimed in claim 6, wherein saidsolubilizing agent is present in an amount of 10 to 75% by weight, saidsolubilizing agent being a glycol ether without hydroxyl groups.
 15. Theprocess as claimed in claim 7, wherein the oxidation is carried out atemperature from 10 to 60°.
 16. The process as claimed in claim 8,wherein the oxidation is carried out at a pH from 6 to 8.5.